Organic Light Emitting Device Comprising Polar Matrix and Metal Dopant

ABSTRACT

The present invention relates to an electronic device comprising at least one light emitting layer between an anode and a cathode, the device further comprising between the cathode and the anode at least one mixed layer comprising (i) in substantially elemental form, an electropositive element selected from Li, Na, K, Be, Sc, Y, La, Lu, Ti and V, and (ii) at least one substantially covalent electron transport matrix compound comprising at least one polar group selected from a phosphine oxide group, wherein the reduction potential of the substantially covalent electron transport matrix compound, if measured by cyclic voltammetry under the same conditions, has the value which is more negative than the value obtained for 4,7-diphenyl-1, 10-phenanthroline, preferably more negative than for (9-phenyI-9II-carbazole-2,7-diyl)bis(diphenylphosphine oxide), more preferably more negative than for (9,9-dihexyI-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highly preferably more negative than for 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferably more negative than for 3-phenyl-3H-benzo[b]dinaphto[2,1-d; 1 2′-fj]phosphepine-3-oxide, most preferably more negative than for pyrene and still preferably more negative than for [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) or a diazole group, wherein the reduction potential of the substantially covalent electron transport matrix compound, if measured by cyclic voltammetry under the same conditions, has the value which is more negative than the value obtained for 4,7-diphenyl-1, 10-phenanthroline, preferably more negative than for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide), more preferably more negative than for (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highly preferably more negative than for 1,3,5-tris(1-phenyl-1 II-benzimidazol-2-yl)benzene, even more preferably more negative than for 3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-fj]phosphepine-3-oxide, most preferably more negative than for pyrene and still preferably more negative than for [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide), a process for manufacturing the same and a compound comprised therein.

The present invention concerns organic light emitting device withimproved electrical properties, particularly the device comprising animproved electron transporting and/or electron injecting layer and/or anOLED stack comprising the improved transporting and/or electroninjecting layer or an improved charge generating layer, process forpreparing the inventive light emitting device, and electron transportmatrix compound applicable in semiconducting material of presentinvention.

I. BACKGROUND OF THE INVENTION

Among the electronic devices comprising at least a part based onmaterial provided by organic chemistry, organic light emitting diodes(OLEDs) have a prominent position. Since the demonstration of efficientOLEDs by Tang et al. in 1987 (C. W. Tang et al., Appl. Phys. Lett. 51(12), 913 (1987)), OLEDs developed from promising candidates to high-endcommercial displays. An OLED comprises a sequence of thin layerssubstantially made of organic materials. The layers typically have athickness in the range of 1 nm to 5μm. The layers are usually formedeither by means of vacuum deposition or from a solution, for example bymeans of spin coating or jet printing.

OLEDs emit light after the injection of charge carriers in the form ofelectrons from the cathode and in form of holes from the anode intoorganic layers arranged in between. The charge carrier injection iseffected on the basis of an applied external voltage, the subsequentformation of excitons in a light emitting zone and the radiativerecombination of those excitons. At least one of the electrodes istransparent or semitransparent, in the majority of cases in the form ofa transparent oxide, such as indium tin oxide (ITO), or a thin metallayer.

Among the matrix compounds used in OLED light emitting layers (LELs) orelectron transporting layers (ETLs), important position have thecompounds that comprise at least one polar group selected from phosphineoxide and diazole. The reason why such polar group often significantlyimproves the electron injecting and/or electron transporting propertiesof the semiconducting material is not yet fully understood. It isbelieved that the high dipole moment of the polar group plays somehowthe positive role. Especially recommended for this use are triarylphosphine oxides comprising at least one condensed aromatic orheteroaromatic group attached directly to the phosphine oxide group, seee.g. JP 4 876 333 B2. Among diazole groups, especiallyphenylbenzimidazole groups have been widely utilized for the design ofnew electron transport matrix compounds, for example TPBI described inU.S. Pat. No. 5,645,948, and some compounds comprising benzimidazolylstructural moieties linked with other structural moieties comprisingdelocalized pi-electrons in two or more aromatic or heteroaromatic ringsnowadays are considered to be industrial standard, e.g. compound LG-201(for example U.S. Pat. No 6,878,469)

Electrical doping of charge transporting semiconducting materials forimproving their electrical properties, especially conductivity, is knownsince 1990s, e.g. from U.S. Pat. No. 5,093,698 A. An especially simplemethod for n-doping in ETLs prepared by the thermal vacuum deposition,which is currently the standard method most frequently used, e.g. inindustrial manufacture of displays, is evaporation of a matrix compoundfrom one evaporation source and of a highly electropositive metal fromanother evaporation source and their co-deposition on a solid substrate.As useful n-dopants in triaryl phosphine oxide matrix compounds, alkalimetals and alkaline earth metals were recommended in JP 4 725 056 B2,with caesium as the dopant successfully used in the given examples.Indeed, caesium as the most electropositive metal offers the broadestfreedom in the choice of a matrix material, and it is likely the reasonwhy solely caesium was the n-doping metal of choice in the citeddocument.

For an industrial use, caesium as a dopant has several seriousdrawbacks. First, it is very reactive, moisture and highly air sensitivematerial that renders any handling difficult and incurs significantadditional costs for mitigating the high safety and fire hazardunavoidably linked with its use. Second, its quite low normal boilingpoint (678° C.) indicates that it may be highly volatile under highvacuum conditions. Indeed, at pressures below 10⁻² Pa used in industrialequipment for vacuum thermal evaporation (VTE), caesium metal evaporatessignificantly already at slightly elevated temperature. Taking intoaccount that the evaporation temperatures for typical matrix compoundsused in organic semiconducting materials at pressures below 10⁻² Pa aretypically between 150-400° C., avoiding an uncontrolled caesiumevaporation, resulting in its undesired deposition contaminating thecolder parts of the whole equipment (e.g. the parts that are shieldedagainst heat radiation from the organic matrix evaporation source), is areally challenging task.

Several methods for overcoming these drawbacks and enabling industrialapplicability of caesium for n-doping in organic electronic devices havebeen published. For safe handling, caesium may be supplied in hermeticshells that open just inside the evacuated evaporation source,preferably during heating to the operational temperature. Such technicalsolution was provided e.g. in WO 2007/065685, however, it does not solvethe problem of caesium high volatility.

U.S. Pat. No. 7,507,694 B2 and EP 1 648 042 B1 offer another solution inform of caesium alloys that melt at low temperature and showsignificantly decreased caesium vapour pressure in comparison with thepure metal. Bismuth alloys of WO2007/109815 that release caesium vapoursat pressures of the order 10⁻⁴ Pa and temperatures up to about 450° C.represent another alternative. Yet, all these alloys are still highlyair and moisture sensitive. Moreover, this solution has further drawbackin the fact that the vapour pressure over the alloy changes with thedecreasing caesium concentration during the evaporation. That createsnew problem of an appropriate deposition rate control, e.g. byprogramming the temperature of the evaporation source. So far, qualityassurance (QA) concerns regarding robustness of such process on anindustrial scale hamper a wider application of this technical solutionin mass production processes.

A viable alternative to Cs doping represent highly electropositivetransition metal complexes like W₂(hpp)₄ that have ionisation potentialscomparably low as caesium and volatilities comparable with volatilitiesof usual organic matrices. Indeed, these complexes disclosed aselectrical dopants first in WO2005/086251 are very efficient for mostelectron transporting matrices except some hydrocarbon matrices. Despitetheir high air and moisture sensitivity, these metal complexes providesatisfactory n-doping solution for an industrial use, if supplied in theshells according to WO 2007/065685. Their main disadvantage is theirhigh price caused by relative chemical complexity of comprised ligandsand necessity of a multistep synthesis of the final complex, as well asadditional costs incurred by necessity of using the protective shellsand/or by the QA and logistic issues linked with shell recycling andrefilling.

Another alternative represent strong n-dopants created in situ in thedoped matrix from relatively stable precursors by an additional energysupplied e.g. in form of ultraviolet (UV) or visible light of anappropriate wavelength. Appropriate compounds for this solution wereprovided e.g. in WO2007/107306 A1. Nevertheless, state-of-art industrialevaporation sources require materials with very high thermal stability,allowing their heating to the operational temperature of the evaporationsource without any decomposition during the whole operating cycle (e.g.,for a week at 300° C.) of the source loaded with the material to beevaporated. Providing organic n-dopants or n-dopant precursors with suchlong-term thermal stability is a real technical challenge so far.Moreover, the complicated arrangement of the production equipment thatmust ensure a defined and reproducible additional energy supply forachieving reproducibly the desired doping level (through the in situactivation of the dopant precursor deposited in the matrix) representsan additional technical challenge and a potential source of additionalCA issues in mass production.

Yook et al (Advanced Functional Materials 2010, 20, 1797-1802)successfully used caesium azide in laboratory as an air-stable Csprecursor. This compound is known to decompose under heating above 300°C. to caesium metal and elemental nitrogen. This process is, however,hardly applicable in contemporary industrial VTE sources, due todifficult control of such heterogeneous decomposition reaction in alarger scale. Moreover, release of nitrogen gas as a by-product in thisreaction brings a high risk that, especially at higher deposition ratesdesired in the mass production, the expanding gas will expel solidcaesium azide particles from the evaporation source, causing thus highdefect counts in the deposited layers of doped semiconducting materials.

Another alternative approach for electrical n-doping in electrontransporting matrices is doping with metal salts or metal complexes. Themost frequently used example of such dopant is lithium8-hydroxy-quinolinolate (LiQ). It is especially advantageous in matricescomprising a phosphine oxide group, see e.g. WO 2012/173370 A2. The maindisadvantage of metal salt dopants is that they improve basically onlyelectron injection to the adjacent layers and do not increase theconductivity of doped layers. Their utilization for decreasing theoperational voltage in electronic devices is thus limited on quite thinelectron injecting or electron transporting layers and does hardly allowe.g. an optical cavity tuning by using ETLs thicker than approximately25 nm, what is well possible with redox-doped ETLs having highconductivity. Furthermore, metal salts typically fail as electricaldopants in cases wherein creation of new charge carriers in the dopedlayer is crucial, e.g. in charge generating layers (CGL, called also p-njunctions) that are necessary for the function of tandem OLEDs.

For the above reasons, and especially for electrical doping in ETLsthicker than approximately 30 nm, the current technical practice preferslithium as an industrial redox n-dopant (see e.g. U.S. Pat. No.6,013,384 B2). This metal is relatively cheap and differs from otheralkali metals by its somewhat lower reactivity and, especially, by itssignificantly lower volatility (normal boiling point about 1340° C.),allowing its evaporation in the VTE equipment at temperatures between350-550° C.

Nevertheless, quite in accordance with its high n-doping power allowingLi to dope majority of usual types of electron transporting matrices,this metal possesses also a high degree of reactivity. It reacts underambient temperature even with dry nitrogen and for its use in a highlyreproducible manufacturing process complying with contemporaryindustrial QA standards, it must be stored and handled exclusively underhigh purity noble gases. Moreover, if Li is co-evaporated with matrixcompounds that have evaporation temperatures in the range 150-300° C.,its significantly higher evaporation temperature in comparison with thematrix evaporation temperature already causes cross-contaminationproblems in the VTE equipment.

Many documents suggest as alternative n-dopants almost any knownmetallic element including weakly reductive and highly volatile Zn, Cd,Hg, weakly reductive Al, Ga, In, Tl, Bi, Sn, Pb, Fe, Co, Ni, or evennoble metals like Ru, Rh, Ir and/or refractory metals with highest knownboiling points like Mo, W, Nb, Zr (see e.g. JP 2009/076508 or WO2009/106068). Unfortunately, not only in these two documents cited hereas examples but throughout the scientific and patent literature overall,there is in fact lack of any evidence that some of these suggestionshave ever been experimentally tested.

To be more specific, even WO 2009/106068 that does not merely mentionall imaginable dopants but really strives to claim all the namedmetalloid elements as n-dopants in organic electronic devices due theiralleged applicability through a high-temperature decomposition of agaseous precursor compound in a heated nozzle, does not bring any singlenumeric value documenting the physical parameters of allegedly prepareddoped materials and/or technical performance of allegedly prepareddevices.

On the other hand, US2005/0042548 published before the date of priorityof WO 2009/106068 teaches in paragraph 0069 (see namely the last twolines of the left column and first three lines of the right column onpage 7) that iron pentacarbonyl can be used for n-doping in organic ETMsif the compound is activated by UV radiation which splits off a carbonmonoxide ligand. The coordinatively unsaturated iron compound thenreacts with the matrix, what results in the observed doping effects. Inthe light of this previous art showing that the metal carbonyls thatwere used in the alleged working example of WO 2009/106068 are knownn-dopants in organic matrices if activated by supply of additionalenergy, it seems quite likely that if the applicants of WO2009/106068really obtained with their jet of iron pentacarbonyl flowing through aceramic nozzle electrically heated to a white glow (see the lastparagraph of the German text on page 12 of the cited PCT application)any doping effect in the target bathocuproin layer, this effect wascaused rather by the same coordinatively unsaturated iron carbonylcomplex as produced by UV irradiation in US2005/0042548, than withelemental iron as they suggest. This suspicion is further supported bythe fourth paragraph on page 13 of the cited PCT application whichteaches that the same result can be obtained with a cold nozzle, if thestream of iron pentacarbonyl is irradiated with an infrared laser havingthe wavelength fitting with the absorption frequency of the CO groups inthe iron pentacarbonyl complex. Here, it is even more likely that thelaser activation resulted not in naked metal atoms or clusters of metalatoms but in a reactive, coordinately unsaturated iron complex stillbearing some carbonyl ligands, analogously to the reactive complexformed by activation with the UV light.

Despite metals with strongly negative standard redox potentials likealkali earth metals or lanthanides are recited as alternative n-dopantsbesides alkali metals basically in each document dealing with redoxn-doping, the record of the proven n-doping with any metal differentfrom alkali metals is very scarce.

Magnesium is in comparison with alkaline metals much less reactive. Itreacts even with liquid water at the ordinary temperature very slowlyand in air it keeps its metallic luster and does not gain weight formonths. It may be thus considered as practically air-stable. Moreover,it has low normal boiling point (about 1100° C.), very promising for itsVTE processing in an optimum temperature range for co-evaporation withorganic matrices.

On the other hand, the authors of the present application confirmed in ascreening done with dozens of state-of-art ETMs that Mg does not possessa sufficient doping strength for common ETMs which are free of stronglypolar groups like phosphine oxide group. The only favourable result hasbeen achieved in OLEDs comprising thin electron injection layersconsisting of a specific kind of triaryl phosphine oxide matrix(comprising a special tris-pyridyl unit designed for chelating metals),doped with magnesium, as shown in EP 2 452 946 A1. Despite thestructural specifity and very favourable (in terms of its LUMO levelwhich is quite deep under the vacuum level in the absolute energy scale)dopability of the exemplary matrix tested with magnesium in EP 2 452 946A1, the positive results achieved with this n-doped semiconductingmaterial encouraged further research focused on n-doping withsubstantially air stable metals.

It is an object of the invention to overcome the drawbacks of the priorart and to provide organic light emitting diodes with bettercharacteristics, especially with low voltage and, more specifically,OLEDs with low voltage and high efficiency, preferably utilizingsubstantially air stable metals as n-dopants, especially in ETMs havingtheir lowest unoccupied molecular orbital (LUMO) energy levels closer tovacuum level than the ETMs which have electrochemical redox potentials(that are in a simple linear relationship with the LUMO levels and aremuch easier measurable than LUMO levels themselves) with more positivevalues than about −2.47 V against ferrocenium/ferrocene reference.

It is a further object of the invention to provide alternative metallicelements which are substantially air stable and can be successfullyembedded (preferably by standard VTE, processes and using contemporaryevaporation sources) in electrically doped semiconducting materials foruse in electronic devices.

A third object of the invention is to provide a process formanufacturing the semiconducting material utilizing substantially airstable metals as n-dopants.

A fourth object of the invention is to provide new matrix compoundsapplicable in semiconducting materials according to the invention.

II. SUMMARY OF THE INVENTION

The object is achieved by an electronic device comprising at least onelight emitting layer between the anode and the cathode, the devicefurther comprising between the cathode and the anode at least one mixedlayer (which may also be referred to as substantially organic layer)comprising

-   -   (i) in substantially elemental form, an electropositive element        selected from Li, Na, K,

Be, Sc, Y, La, Lu, Ti and V, and

-   -   (ii) at least one substantially covalent electron transport        matrix compound comprising at least one polar group selected        from        -   a) phosphine oxide group,

wherein the reduction potential of the electron transport matrixcompound, if measured by cyclic voltammetry under the same conditions,has the value which is more negative than the value obtained for4,7-diphenyl-1,10-phenanthroline, preferably more negative than for(9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide), morepreferably more negative than for(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highlypreferably more negative than for1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferablymore negative than for3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, mostpreferably more negative than for pyrene and still preferably morenegative than for [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphineoxide) or

-   -   -   b) diazole group,

wherein the reduction potential of the substantially covalent electrontransport matrix compound, if measured by cyclic voltammetry under thesame conditions, has the value which is more negative than the valueobtained for 4,7-diphenyl-1,10-phenanthroline, preferably more negativethan for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),more preferably more negative than for(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highlypreferably more negative than for1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferablymore negative than for3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, mostpreferably more negative than for pyrene and still preferably morenegative than for [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphineoxide).

It is to be understood that “substantially covalent” means compoundscomprising elements bound together mostly by covalent bonds. Examples ofsubstantially covalent molecular structures may be organic compounds,organometallic compounds, metal complexes comprising polyatomic ligands,metal salts of organic acids. In this sense, the term “substantiallyorganic layer” is to be understood as a layer comprising a substantiallycovalent electron transport matrix compound.

It is further understood that the term “substantially covalent compound”encompasses materials which can be processed by usual techniques andequipment for manufacturing organic electronic devices, like vacuumthermal evaporation or solution processing. It is clear that purelyinorganic crystalline or glassy semiconducting materials like silicon orgermanium which cannot be, due to their extreme high vaporizationtemperatures and insolubility in solvents, prepared in equipment fororganic electronic devices, are not encompassed by the term“substantially covalent compound.

Preferably, the phosphine oxide polar group is part of a substantiallycovalent structure comprising at least three carbon atoms directlyattached to the phosphorus atom of the phosphine oxide group and havingoverall count of covalently bound atoms, preferably selected from C, H,B, Si, N, P, O, S, F, Cl, Br and I, in the range 16-250, more preferablyin the range 32-220, even more preferably in the range 48-190, mostpreferably in the range 64-160.

Also preferably, the electron transport matrix compound comprises aconjugated system of at least ten delocalized electrons.

Examples of conjugated systems of delocalized electrons are systems ofalternating pi- and sigma bonds. Optionally, one or more two-atomstructural units having the pi-bond between its atoms can be replaced byan atom bearing at least one lone electron pair, typically by a divalentatom selected from O, S, Se, Te or by a trivalent atom selected from N,P, As, Sb, Bi. Preferably, the conjugated system of delocalizedelectrons comprises at least one aromatic ring adhering to the Hückelrule.

More preferably, the substantially covalent electron transport matrixcompound comprises at least two aromatic or heteroaromatic rings whichare either linked by a covalent bond or condensed. Also preferably, thephosphine oxide polar group is selected from phosphine oxide substitutedwith three monovalent hydrocarbyl groups or one divalent hydrocarbylenegroup forming with the phosphorus atom a ring and one monovalenthydrocarbyl group, and the overall count of carbon atoms in thehydrocarbyl groups and the hydrocarbylene group is 8-80, preferably14-72, more preferably 20-66, even more preferably 26-60, mostpreferably 32-54. In another preferred embodiment, there are twosubstantially covalent compounds comprised in the semiconductingmaterial, the first compound comprising the polar group selected fromthe phosphine oxide group and the diazole group, wherein the firstcompound is free of a conjugated system of delocalized electrons, ordoes comprise a conjugated system of less than 10 delocalized electrons;and the second compound that does comprise a conjugated system of atleast 10 delocalized electrons. More preferably, the second compound isfree of a polar group selected from the phosphine oxide group and/or thediazole group.

Examples of compounds comprising a condensed aromatic skeletoncomprising at least 10 delocalized electrons are e.g. naphthalene,anthracene, phenanthrene, pyrene, quinoline, indole or carbazole. Theconjugated system of delocalized electrons may also consist of at leasttwo directly attached aromatic rings, the simplest examples of suchsystems being biphenyl, bithienyl, phenylthiophene, phenylpyridine andlike. On the other hand, it is known that a pentavalent phosphorus atom,for example the phosphorus atom in the phosphine oxide group, does notparticipate in conjugation in systems of delocalized electrons attachedto the pentavalent P atom, and in this sense resembles sp³ hybridizedcarbon, for example the carbon atom in a methylene group. Mostpreferably, the conjugated system of at least 10 delocalized electronscomprised in the second compound is comprised in a C₁₄-C₅₀-arene or aC₈-C₅₀ heteroarene structural moiety, wherein the overall count ofcarbon atoms comprises also possible substituents. It is in the spiritof the present invention that the count, topology and spatialarrangement of the substituents on the structural moiety comprising theconjugated system of delocalized electrons is not decisive for thefunction of the invention. Preferred heteroatoms in the heteroarenestructural moiety are B, O, N and S. In the second compound, both thecore atoms bearing the comprised system of delocalized electrons as wellas the polyvalent atoms like C, Si, B, which preferably form theperipheral substituents attached to the core atoms, may be substitutedwith terminal atoms of elements which are typically monovalent inorganic compounds and which are more preferably selected from H, F, Cl,Br and I. The conjugated system of at least 10 delocalized electrons ispreferably comprised in a C₁₄-C₅₀-arene or a C₈-C₅₀ heteroarenestructural moiety. Also preferably, the diazole polar group is animidazole group. In one of preferred embodiments, the electronic devicefurther comprises a metal salt additive consisting of at least one metalcation and at least one anion. Preferably, the metal cation is Li⁺ orMg²⁺. Also preferably, the metal salt additive is selected from metalcomplexes comprising a 5-, 6- or 7-membered ring that contains anitrogen atom and an oxygen atom attached to the metal cation and fromcomplexes having the structure according to formula (II)

wherein A¹ is a C₆-C₃₀ arylene or C₂-C₃₀ heteroarylene comprising atleast one atom selected from O, S and N in an aromatic ring and each ofA² and A³ is independently selected from a C₆-C₃₀ aryl and C₂-C₃₀heteroaryl comprising at least one atom selected from O, S and N in anaromatic ring. Equally preferably, the anion is selected from the groupconsisting of phenolate substituted with a phosphine oxide group,8-hydroxyquinolinolate and pyrazolylborate. The metal salt additivepreferably works as a second electrical n-dopant, more preferably, itworks synergistically with the metallic element present in the elementalform and works as the first electrical n-dopant.

It is preferred that the electropositive element is selected from Li, Scand Y. Preferably, the molar ratio of the electropositive element to thefirst compound is lower than 0.5, preferably lower than 0.4, morepreferably lower than 0.33, even more preferably lower than 0.25, evenmore preferably lower than 0.20, even more preferably lower than 0.17,most preferably lower than 0.15, still preferably lower than 0.13, stillbut less preferably lower than 0.10.

It is further preferred that the molar ratio of the electropositiveelement to the first compound is higher than 0.01, preferably higherthan 0.02, more preferably higher than 0.03, even more preferably higherthan 0.05, most preferably higher than 0.08.

Preferably, the electropositive element is comprised in an electrontransporting, electron injecting, or charge generating layer. Morepreferably, the electron transporting or electron injecting layer isadjacent to a layer consisting of compounds that have their reductionpotentials, if measured by cyclic voltammetry under the same conditions,more negative than the electron transport matrix compounds of theadjacent electron transporting or electron injecting layer. In one ofpreferred embodiments, the layer adjacent to the layer made of inventivesemiconducting material is the emitting layer.

It is further preferred that the light emitting layer emits blue orwhite light. In one of preferred embodiments, the light emitting layercomprises at least one polymer. More preferably, the polymer is a bluelight emitting polymer.

Also preferably, the electron transporting or electron injecting layeris thicker than 5 nm, preferably thicker than 10 nm, more preferablythicker than 15 nm, even more preferably thicker than 20 nm, mostpreferably thicker than 25 nm, still preferably thicker than 50 nm, andstill preferably thicker than 100 nm.

In one of preferred embodiments, the electron transporting or electroninjecting layer is adjacent to a cathode consisting of a semiconductingmetal oxide. Preferably, the semiconducting metal oxide is indium tinoxide. Also preferably, the cathode is prepared by sputtering.

Still another embodiment of the invention is a tandem OLED stackcomprising a metal-doped pn-junction comprising

-   -   (1) in substantially elemental form, an electropositive element        selected from Li, Na, K, Be, Sc, Y, La, Lu, Ti and V, and    -   (ii) at least one substantially covalent electron transport        matrix compound comprising at least one polar group selected        from        -   a) phosphine oxide group,

wherein the reduction potential of the substantially covalent electrontransport matrix compound, if measured by cyclic voltammetry under thesame conditions, has the value which is more negative than the valueobtained for 4,7-diphenyl-1,10-phenanthroline, preferably more negativethan for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),more preferably more negative than for(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highlypreferably more negative than for 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferably more negative than for3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, mostpreferably more negative than for pyrene and still preferably morenegative than for [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphineoxide) or

-   -   -   b) diazole group,

    -   wherein the reduction potential of the substantially covalent        electron transport matrix compound, if measured by cyclic        voltammetry under the same conditions, has the value which is        more negative than the value obtained for        4,7-diphenyl-1,10-phenanthroline, preferably more negative than        for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine        oxide), more preferably more negative than for        (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),        highly preferably more negative than for        1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more        preferably more negative than for        3-phenyl-3H-benzo[b]dinaphto[2,1-d:2′-f]phosphepine-3-oxide,        most preferably more negative than for pyrene and still        preferably more negative than for        [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide).

The second object of the invention is achieved by using a metal selectedfrom Na, K, Be, Sc, Y, La, Lu, Ti and V as an electrical n-dopant inorganic light emitting diodes, specifically in diodes comprising, as amatrix n-doped with these electropositive metals, an electron transportmatrix compound comprising at least one polar group selected from

-   -   -   a) phosphine oxide group,

    -   wherein the reduction potential of the organic electron        transport matrix compound, if measured by cyclic voltammetry        under the same conditions, has the value which is more negative        than the value obtained for 4,7-diphenyl-1,10-phenanthroline,        preferably more negative than for        (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),        more preferably more negative than for        (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),        highly preferably more negative than for        1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more        preferably more negative than for        3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide,        most preferably more negative than for pyrene and still        preferably more negative than for        [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) or        -   b) diazole group,

    -   wherein the reduction potential of the organic electron        transport matrix compound, if measured by cyclic voltammetry        under the same conditions, has the value which is more negative        than the value obtained for 4,7-diphenyl-1,10-phenanthroline,        preferably more negative than for        (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),        more preferably more negative than for        (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),        highly preferably more negative than for        1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more        preferably more negative than for        3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide,        most preferably more negative than for pyrene and still        preferably more negative than for        [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide).

The third object of the invention is achieved by process formanufacturing the electronic device comprising, between the cathode andthe anode, at least one light emitting layer and at least onesubstantially organic layer, the process comprising at least one stepwherein

-   -   (i) an electropositive element selected from Li, Na, K, Be, Sc,        Y, La, Lu, Ti and V, and    -   (ii) at least one substantially covalent electron transport        matrix compound comprising at least one polar group selected        from        -   a) phosphine oxide group,    -   wherein the reduction potential of the substantially covalent        electron transport matrix compound, if measured by cyclic        voltammetry under the same conditions, has the value which is        more negative than the value obtained for        4,7-diphenyl-1,10-phenanthroline, preferably more negative than        for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine        oxide), more preferably more negative than for        (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),        highly preferably more negative than for        1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more        preferably more negative than for        3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide,        most preferably more negative than for pyrene and still        preferably more negative than for        [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) or b)        diazole group,    -   wherein the reduction potential of the substantially covalent        electron transport matrix compound, if measured by cyclic        voltammetry under the same conditions, has the value which is        more negative than the value obtained for        4,7-diphenyl-1,10-phenanthroline, preferably more negative than        for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine        oxide), more preferably more negative than for        (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),        highly preferably more negative than for        1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more        preferably more negative than for        3-phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide,        most preferably more negative than for pyrene and still        preferably more negative than for        [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide),

are coevaporated and codeposited under reduced pressure to form thesubstantially organic layer, and the electropositive element isdeposited in its elemental or substantially elemental form. Preferably,the electropositive element is evaporated from its elemental orsubstantially elemental form, more preferably from a substantially airstable elemental or substantially elemental form. Also preferably, thepressure is lower than 10⁻² Pa, more preferably lower than 10⁻³ Pa, mostpreferably lower than 10⁻⁴ Pa.

Preferably, the electropositive element has normal boiling point lowerthan 3000° C., more preferably lower than 2200° C., even more preferablylower than 1800° C., most preferably lower than 1500° C. Under normalboiling point, it is to be understood the boiling point at normalatmospheric pressure (101.325 kPa).

In one embodiment, the electropositive element is Li and the ratio ofmass deposition rate of Li to overall mass deposition rate of theelectron transport matrix is maintained within the range 0.0005-0.0080,preferably within the range 0.0010-0.0075, more preferably within therange 0.0015-0.0070, even more preferably within the range0.0020-0.0065, most preferably within the range 0.0025-0.0060, and stillpreferably within the range 0.0030-0.0050.

It is to be understood that the term “substantially air stable” refersto metals and their substantially elemental form (e.g. alloys with othermetals) which reacts under ambient conditions with atmospheric gases andmoisture slowly enough to avoid quality assurance issues if it ishandled under ambient conditions in an industrial process. Morespecifically, a form of a metal shall be assigned as substantially airstable for the purposes of this application, if a sample of this formhaving the weight at least 1 g and a surface exposed to air at least 1cm² may be kept under standard temperature 25° C., pressure 101 325 Paand relative humidity 80% for at least an hour, preferably for at least4 hours, more preferably for at least 24 hours, and most preferably forat least 240 hours, without showing a statistically significant weightgain, provided that the accuracy of weighing is at least 0.1 mg.

Most preferably, the electropositive element is evaporated from a linearevaporation source. The first object of the invention is achieved alsoby electronic device preparable by any of the above described processesaccording to invention. The fourth object of the invention is achievedby compound having the structure according to formula (I)

III. BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic illustration of a device in which the presentinvention can be incorporated.

FIG. 2 shows a schematic illustration of a device in which the presentinvention can be incorporated.

FIG. 3 shows absorbance curves of two n-doped semiconducting materials;circles stand for comparative matrix compound C10 doped with 10 wt % ofcompound F1 that forms strongly reducing radicals, triangles stand forcompound E10 doped with 5 wt % Mg.

IV. DETAILED DESCRIPTION OF THE INVENTION Device Architecture

FIG. 1 shows a stack of anode (10), organic semiconducting layer (11)comprising the light emitting layer, electron transporting layer (ETL)(12), and cathode (13). Other layers can be inserted between thosedepicted, as explained herein.

FIG. 2 shows a stack of an anode (20), a hole injecting and transportinglayer (21), a hole transporting layer (22) which can also aggregate thefunction of electron blocking, a light emitting layer (23), an ETL (24),and a cathode (25). Other layers can be inserted between those depicted,as explained herein.

The wording “device” comprises the organic light emitting diode.

Material properties—energy levels

A method to determine the ionization potentials (IP) is the ultravioletphoto spectroscopy (UPS). It is usual to measure the ionizationpotential for solid state materials; however, it is also possible tomeasure the IP in the gas phase. Both values are differentiated by theirsolid state effects, which are, for example the polarization energy ofthe holes that are created during the photo ionization process. Atypical value for the polarization energy is approximately 1 eV, butlarger discrepancies of the values can also occur. The IP is related toonset of the photoemission spectra in the region of the large kineticenergy of the photoelectrons, i.e. the energy of the most weakly boundedelectrons. A related method to UPS, the inverted photo electronspectroscopy (IPES) can be used to determine the electron affinity (EA).However, this method is less common. Electrochemical measurements insolution are an alternative to the determination of solid stateoxidation (E_(ox)) and reduction (E_(red)) potential. An adequate methodis, for example, cyclic voltammetry. To avoid confusion, the claimedenergy levels are defined in terms of comparison with referencecompounds having well defined redox potentials in cyclic voltammetry,when measured by a standardized procedure. A simple rule is very oftenused for the conversion of redox potentials into electron affinities andionization potential: IP (in eV)=4.8 eV+e*E_(ox) (wherein E_(ox) isgiven in volts vs. ferrocenium/ferrocene (Fc⁺/Fc)) and EA (in eV)=4.8eV+e*E_(red) (E_(red) is given in volts vs. Fc⁺/Fc) respectively (see B.W. D'Andrade, Org. Electron. 6, 11-20 (2005)), e* is the elementalcharge. Conversion factors for recalculation of the electrochemicalpotentials in the case other reference electrodes or other referenceredox pairs are known (see A. J. Bard, L. R. Faulkner, “ElectrochemicalMethods: Fundamentals and Applications”, Wiley, 2. Ausgabe 2000). Theinformation about the influence of the solution used can be found in N.G. Connelly et al., Chem. Rev. 96, 877 (1996). It is usual, even if notexactly correct, to use the terms “energy of the HOMO” E_((HOMO)) and“energy of the LUMO” E_((LUMO)), respectively, as synonyms for theionization energy and electron affinity (Koopmans Theorem). It has to betaken into consideration that the ionization potentials and the electronaffinities are usually reported in such a way that a larger valuerepresents a stronger binding of a released or of an absorbed electron,respectively. The energy scale of the frontier molecular orbitals (HOMO,LUMO) is opposed to this. Therefore, in a rough approximation, thefollowing equations are valid: IP=−E_((HOMO)) and EA=E_((LUMO)) (thezero energy is assigned to the vacuum).

For the chosen reference compounds, the inventors obtained followingvalues of the reduction potential by standardized cyclic voltammetry intetrahydrofuran (THF) solution vs. Fc⁺/Fc:

Examples of matrix compounds for state-of-art electrically dopedsemiconducting materials based on matrix compounds comprising phosphineoxide group and a conjugated system of at least 10 delocalized electronsare

Another suitable class of matrix compounds appropriate for the presentinvention represent compounds comprising at least one phosphepine ringand having the phosphorus atom of the phosphepine ring substituted withat least one monovalent substituent R, wherein the phosphepine ring is aring according to formula (IV)

structural moieties A, B, C are independently selected fromunsubstituted ortho-phenylene and ortho-phenylene substituted with up tofour electron donating groups,

R is selected from

-   -   (i) substituted phenyl and phenyl substituted with up to five        substituents independently selected from electron donating        groups, or    -   (ii) H and electron donating groups.

Preferably, the electron donating group is selected from alkyl,heteroalkyl, alkoxy, alkylthio, phenoxy, phenylthio, diphenylphosphinyl,and from disubstituted amino group wherein the substituents on thenitrogen atom of the amino group are independently selected from phenyland alkyl.

Also preferably, the electron donating group comprises up to 30 carbonatoms. More preferably, the matrix compound comprising at least onephosphepine ring comprises at least one phosphepine group, even morepreferably, the phosphepine ring is a phosphepine-P-oxide ring.

Example of such simple phosphepine matrix compounds having hughlynegative redox potential is compound E16, which (if measured by CVprocedure described below) redox potential vs Fc⁺/Fc −2.91 V

Substrate

It can be flexible or rigid, transparent, opaque, reflective, ortranslucent. The substrate should be transparent or translucent if thelight generated by the OLED is to be transmitted through the substrate(bottom emitting). The substrate may be opaque if the light generated bythe OLED is to be emitted in the direction opposite of the substrate,the so called top-emitting type. The OLED can also be transparent. Thesubstrate can be either arranged adjacent to the cathode or anode.

Electrodes

The electrodes are the anode and the cathode, they must provide acertain amount of conductivity, being preferentially conductors.Preferentially the “first electrode” is the cathode. At least one of theelectrodes must be semi-transparent or parent to enable the lighttransmission to the outside of the device. Typical electrodes are layersor a stack of layer, comprising metal and/or transparent conductiveoxide. Other possible electrodes are made of thin busbars (e.g. a thinmetal grid) wherein the space between the busbars is filled (coated)with a transparent material having certain conductivity, such asgraphene, carbon nanotubes, doped organic semiconductors, etc.

In one embodiment, the anode is the electrode closest to the substrate,which is called non-inverted structure. In another mode, the cathode isthe electrode closest to the substrate, which is called invertedstructure.

Typical materials for the Anode are ITO and Ag. Typical materials forthe cathode are Mg:Ag (10 vol % of Mg), Ag, ITO, Al. Mixtures andmultilayer cathodes are also possible.

Preferably, the cathode comprises a metal selected from Ag, Al, Mg, Ba,Ca, Yb, In, Zn, Sn, Sm, Bi, Eu, Li, more preferably from Al, Mg, Ca, Baand even more preferably selected from Al or Mg. Preferred is also acathode comprising an alloy of Mg and Ag.

It is one of the advantages of the present invention that it enablesbroad selection of cathode materials. Besides metals with low workfunction which are in most cases necessary for good performance ofdevices comprising the state-of-the-art n-doped ETL materials, alsoother metals or conductive metal oxides may be used as cathodematerials. Especially advantageous is the use of cathodes prepared ofmetallic silver, because neat silver provides the best reflectivity, andthus best efficiency, specifically e.g. in bottom emitting devices builton a transparent substrate and having an a transparent conductive oxideanode. Neat silver cathodes are not built into devices having undopedETLs or ETLs doped with metal salt additives, because such devices showhigh operational voltages and low efficiencies due to poor electroninjection.

It is equally well possible that the cathode is pre-formed on asubstrate (then the device is an inverted device), or the cathode in anon-inverted device is formed by vacuum deposition of a metal or bysputtering.

Hole-Transporting Layer (HTL)

The HTL is a layer comprising a large gap semiconductor responsible totransport holes from the anode or holes from a CGL to the light emittinglayer (LEL). The HTL is comprised between the anode and the LEL orbetween the hole generating side of a CGL and the LEL. The HTL can bemixed with another material, for example a p-dopant, in which case it issaid the HTL is p-doped. The HTL can be comprised by several layers,which can have different compositions. P-doping of the HTL lowers itsresistivity and avoids the respective power loss due to the otherwisehigh resistivity of the undoped semiconductor. The doped HTL can also beused as optical spacer, because it can be made very thick, up to 1000 nmor more without significant increase in resistivity.

Suitable hole transport matrices (HTM) can be, for instance compoundsfrom the diamine class, where a delocalized pi-electron systemconjugated with lone electron pairs on the nitrogen atoms is provided atleast between the two nitrogen atoms of the diamine molecule. ExamplesareN4,N4′-di(naphthalen-1-yl)-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(HTM1), N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′,1″-terphenyl]-4,4″-diamine(HTM2). The synthesis of diamines is well described in literature; manydiamine HTMs are readily commercially available.

Hole-Injecting Layer (HIL)

The HIL is a layer which facilitates the injection of holes from theanode or from the hole generating side of a CGL into an adjacent HTL.Typically, the HIL is a very thin layer (<10 mm). The hole injectionlayer can be a pure layer of p-dopant and can be about 1 nm thick. Whenthe HTL is doped, an HIL may not be necessary, since the injectionfunction is already provided by the HTL.

Light-Emitting Layer (LEL)

The light emitting layer must comprise at least one emission materialand can optionally comprise additional layers. If the LEL comprises amixture of two or more materials the charge carrier injection can occurin different materials for instance in a material which is not theemitter, or the charge carrier injection can also occur directly intothe emitter. Many different energy transfer processes can occur insidethe LEL or adjacent LELs leading to different types of emission. Forinstance excitons can be formed in a host material and then betransferred as singlet or triplet excitons to an emitter material whichcan be singlet or triplet emitter which then emits light. A mixture ofdifferent types of emitter can be provided for higher efficiency. Whitelight can be realized by using emission from an emitter host and anemitter dopant. In one of preferred embodiments of the invention, thelight emitting layer comprises at least one polymer.

Blocking layers can be used to improve the confinement of chargecarriers in the LEL, these blocking layers are further explained in U.S.Pat. No. 7,074,500 B2.

Electron-Transporting Layer (ETL)

The ETL is a layer comprising a large gap semiconductor responsible forelectron transport from the cathode or electrons from a CGL or EIL (seebelow) to the LEL. The ETL is comprised between the cathode and the LELor between the electron generating side of a CGL and the LEL The ETL canbe mixed with an electrical n-dopant, in which case it is said the ETLis n-doped. The ETL can be comprised by several layers, which can havedifferent compositions. Electrical n-doping the ETL lowers itsresistivity and/or improves its ability to inject electrons into anadjacent layer and avoids the respective power loss due to the otherwisehigh resistivity (and/or bad injection ability) of the undopedsemiconductor. If the used electrical doping creates new charge carriersin the extent that substantially increases conductivity of the dopedsemiconducting material in comparison with the undoped ETM, then thedoped ETL can also be used as optical spacer, because it can be madevery thick, up to 1000 nm or more without significant increase in theoperational voltage of the device comprising such doped ETL. Thepreferable mode of electrical doping that is supposed to create newcharge carriers is so called redox doping. In case of n-doping, theredox doping corresponds to the transfer of an electron from the dopantto a matrix molecule.

In case of electrical n-doping with metals used as dopants in theirsubstantially elemental form, it is supposed that the electron transferfrom the metal atom to the matrix molecule results in a metal cation andan anion radical of the matrix molecule. Hopping of the single electronfrom the anion radical to an adjacent neutral matrix molecule is thecurrently supposed mechanism of charge transport in redox n-dopedsemiconductors.

It is, however, hard to understand all properties of semiconductorsn-doped with metals and, specifically, of semiconducting materials ofpresent invention, in terms of electrical redox doping. It is thereforesupposed that semiconducting materials of present inventionadvantageously combine redox doping with yet unknown favourable effectsof mixing ETMs with metal atoms and/or their clusters. It is supposedthat semiconducting materials of present invention contain a significantpart of the added electropositive element in its substantially elementalform. The term “substantially elemental” shall be understood as a formthat is, in terms of electronic states and their energies, closer to thestate of a free atom or to the state of a cluster of metal atoms than tothe state of a metal cation or to the state of a positively chargedcluster of metal atoms.

Without being limited by theory, it can be supposed that there is animportant difference between the n-doped organic semiconductingmaterials of previous art and the n-doped semiconducting materials ofthe present invention. In common organic ETMs of previous art (havingreduction potentials roughly in the range between −2.0 and −3.0 V vs.Fc⁺/Fc and comprising a conjugated system of at least ten delocalizedelectrons), the strong redox n-dopants like alkali metals or W₂(hpp)₄are supposed to create the amounts of charge carriers that arecommensurate to the number of individual atoms or molecules of the addeddopant, and there is indeed an experience that increasing the amount ofsuch strong dopant in conventional matrices above certain level does notbring any substantial gain in electrical properties of the dopedmaterial.

On the other hand, it is difficult to speculate which role shall then-doping strength of the electropositive element play in the matrices ofthe present invention comprising primarily the polar groups but onlyvery small or none conjugated systems of delocalized electrons.

It may be perhaps be supposed that in such matrices, even for thestrongest electropositive element like alkali metals, only part of addedatoms of the electropositive element added as the n-dopant reacts withmatrix molecules by the redox mechanism under formation correspondingmetal cations. It is rather supposed that even in high dilution, whenthe amount of the matrix is substantially higher than the amount ofadded metallic element, a substantial part of the metallic element ispresent in a substantially elemental form. It is further supposed thatif the metallic element of the present invention is mixed with matrix ofthe present invention in a comparable amount, the majority of the addedmetallic element is present in the resulting doped semiconductingmaterial in the substantially elemental form. This hypothesis seems toprovide a reasonable explanation as to why the metallic elements of thepresent invention can be effectively used in significantly broader rangeof ratios to the doped matrix than the stronger dopants of previous art,even though they are weaker dopants. The applicable content of themetallic element in the doped semiconducting material of the presentinvention is roughly in the range from 0.5 weight % up to 25 weight %,preferably in the range from 1 to 20 weight %, more preferably in therange from 2 to 15 weight %, most preferably in the range from 3 to 10weight %.

Hole blocking layers and electron blocking layers can be employed asusual.

Other layers with different functions can be included, and the devicearchitecture can be adapted as known by the skilled in the art. Forexample, an Electron-Injecting Layer (EIL) made of metal, metal complexor metal salt can be used between the cathode and the ETL.

Charge Generation Layer (CGL)

The OLED can comprise a CGL which can be used in conjunction with anelectrode as inversion contact, or as connecting unit in stacked OLEDs.A CGL can have the most different configurations and names, examples arepn-j unction, connecting unit, tunnel junction, etc. Best examples arepn-junctions as disclosed in US 2009/0045728 A1, US 2010/0288362 A1.Metal layers and or insulating layers can also be used.

Stacked OLEDs

When the OLED comprises two or more LELs separated by CGLs, the OLED iscalled a stacked OLED, otherwise it is called a single unit OLED. Thegroup of layers between two closest CGLs or between one of theelectrodes and the closest CGL is called a electroluminescent unit(ELU). Therefore, a stacked OLED can be described asanode/ELU₁/{CGL_(X)/ELU_(1+X)}_(X)/cathode, wherein x is a positiveinteger and each CGL_(x) or each ELU_(1+X) can be equal or different.The CGL can also be formed by the adjacent layers of two ELUs asdisclosed in US2009/0009072 A1. Further stacked OLEDs are described e.g.in US 2009/0045728 A1, US 2010/0288362 A1, and references therein.

Deposition of Organic Layers

Any organic semiconducting layers of the inventive display can bedeposited by known techniques, such as vacuum thermal evaporation (VTE),organic vapour phase deposition, laser induced thermal transfer, spincoating, blade coating, slot dye coating, inkjet printing, etc. Apreferred method for preparing the OLED according to the invention isvacuum thermal evaporation. Polymeric materials are preferably processedby coating techniques from solutions in appropriate solvents.

Preferably, the ETL is formed by evaporation. When using an additionalmaterial in the ETL, it is preferred that the ETL is formed byco-evaporation of the electron transporting matrix (ETM) and theadditional material. The additional material may be mixed homogeneouslyin the ETL. In one mode of the invention, the additional material has aconcentration variation in the ETL, wherein the concentration changes inthe direction of the thickness of the stack of layers. It is alsoforeseen that the ETL is structured in sub-layers, wherein some but notall of these sub-layers comprise the additional material.

In is supposed that semiconducting material of present inventioncontains a significant part of the added electropositive element in itssubstantially elemental form. Consequently, the process of the presentinvention requires that the electropositive element is vaporized fromits elemental or substantially elemental form. In this context, the term“substantially elemental” shall be understood as a form that is, interms of electronic states and their energies and in terms of chemicalbonds, closer to the form of an elemental metal, of a free metal atom orto the form of a cluster of metal atoms, than to the form of a metalsalt, of a covalent metal compound, or to the form of a coordinationcompound of a metal. Typically, metal vapour release from metal alloysaccording to EP 1 648 042 B1 or WO2007/09815 is understood as theevaporation from a substantially elemental form of the evaporated metal.

Electrical Doping

The most reliable and, at the same time, efficient OLEDs are OLEDscomprising electrically doped layers. Generally, the electrical dopingmeans improving of electrical properties, especially the conductivityand/or injection ability of a doped layer in comparison with neatcharge-transporting matrix without a dopant. In the narrower sense,which is usually called redox doping or charge transfer doping, holetransport layers are doped with a suitable acceptor material (p-doping)or electron transport layers with a donor material (n-doping),respectively. Through redox doping, the density of charge carriers inorganic solids (and therefore the conductivity) can be increasedsubstantially. In other words, the redox doping increases the density ofcharge carriers of a semiconducting matrix in comparison with the chargecarrier density of the undoped matrix. The use of doped charge-carriertransport layers (p-doping of the hole transport layer by admixture ofacceptor-like molecules, n-doping of the electron transport layer byadmixture of donor-like molecules) in organic light-emitting diodes is,e.g., described in US 2008/203406 and U.S. Pat. No. 5,093,698.

US2008227979 discloses in detail the charge-transfer doping of organictransport materials, with inorganic and with organic dopants. Basically,an effective electron transfer occurs from the dopant to the matrixincreasing the Fermi level of the matrix. For an efficient transfer in ap-doping case, the LUMO energy level of the dopant is preferably morenegative than the HOMO energy level of the matrix or at least not morethan slightly more positive, preferably not more than 0.5 eV morepositive than the HOMO energy level of the matrix. For the n-dopingcase, the HOMO energy level of the dopant is preferably more positivethan the LUMO energy level of the matrix or at least not more thanslightly more negative, preferably not more than 0.5 eV lower comparedto the LUMO energy level of the matrix. It is furthermore desired thatthe energy level difference for energy transfer from dopant to matrix issmaller than +0.3 eV.

Typical examples of known redox doped hole transport materials are:copper phthalocyanine (CuPc), which HOMO level is approximately −5.2 eV,doped with tetrafluoro-tetracyanoquinonedimethane (F4TCNQ), which LUMOlevel is about −5.2 eV; zinc phthalocyanine (ZnPc) (HOMO=−5.2 eV) dopedwith F4TCNQ; α-NPD(N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine) doped withF4TCNQ. α-NPD doped with 2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (PD1). α-NPD doped with2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile)(PD2). All p-doping in the device examples of the present applicationwas done with 3 mol % of PD2.

Typical examples of known redox doped electron transport materials are:fullerene C60 doped with acridine orange base (AOB);perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) dopedwith leuco crystal violet;2,9-di(phenanthren-9-yl)-4,7-diphenyl-1,10-phenanthroline doped withtetrakis (1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato)ditungsten (II) (W₂(hpp)₄); naphthalene tetracarboxylic aciddi-anhydride (NTCDA) doped with 3,6-bis-(dimethyl amino)-acridine; NTCDAdoped with bis(ethylene-dithio) tetrathiafulvalene (BEDT-TTF).

Besides the redox dopants, certain metal salts can be alternatively usedfor electrical n-doping resulting in lowering operational voltage indevices comprising the doped layers in comparison with the same devicewithout metal salt. True mechanism how these metal salts, sometimescalled “electrically doping additives”, contribute to the lowering ofthe voltage in electronic devices, is not yet known. It is believed thatthey change potential barriers on the interfaces between adjacent layersrather than conductivities of the doped layers, because their positiveeffect on operational voltages is achieved only if layers doped withthese additives are very thin. Usually, the electrically undoped oradditive doped layers are thinner than 50 nm, preferably thinner than 40nm, more preferably thinner than 30 nm, even more preferably thinnerthan 20 nm, most preferably thinner than 15 nm. If the manufacturingprocess is precise enough, the additive doped layers can beadvantageously made thinner than 10 nm or even thinner than 5 nm.

Typical representatives of metal salts which are effective as secondelectrical dopants in the present invention are salts comprising metalcations bearing one or two elementary charges. Favourably, salts ofalkali metals or alkaline earth metals are used. The anion of the saltis preferably an anion providing the salt with sufficient volatility,allowing its deposition under high vacuum conditions, especially in thetemperature and pressure range which is comparable with the temperatureand pressure range suitable for the deposition of the electrontransporting matrix.

Example of such anion is 8-hydroxyquinolinolate anion. Its metal salts,for example lithium 8-hydroxyquinolinolate (LiQ) represented by theformula D1

are well known as electrically doping additives.

Another class of metal salts useful as electrical dopants in electrontransporting matrices of the present invention represent compoundsdisclosed in the application PCT/EP2012/074127 (WO2013/079678), havinggeneral formula (II)

wherein A¹ is a C₆-C₂₀ arylene and each of A²-A³ is independentlyselected from a C₆-C₂₀ aryl, wherein the aryl or arylene may beunsubstituted or substituted with groups comprising C and H or with afurther LiO group, provided that the given C count in an aryl or arylenegroup includes also all substituents present on the said group. It is tobe understood that the term substituted or unsubstituted arylene standsfor a divalent radical derived from substituted or unsubstituted arene,wherein the both adjacent structural moieties (in formula (I), the OLigroup and the diaryl prosphine oxide group) are attached directly to anaromatic ring of the arylene group. In examples of the presentapplication, this class of dopants is represented by compound D2

wherein Ph is phenyl.

Yet another class of metal salts useful as electrical dopants inelectron transporting matrices of the present invention representcompounds disclosed in the application PCT/EP2012/074125(WO2013/079676), having general formula (III)

wherein M is a metal ion, each of A⁴-A⁷ is independently selected fromH, substituted or unsubstituted C₆-C₂₀ aryl and substituted orunsubstituted C₂-C₂₀ heteroaryl and n is valence of the metal ion. In exs pies of the present application, this class of dopants is representedby compound D3

V. ADVANTAGEOUS EFFECT OF THE INVENTION

The favourable effects of the inventive electrically dopedsemiconducting materials are shown by comparison with analogousinventive materials and devices described by applicants in theirprevious application, published as WO2015/097232 A1. The used devicesare described in detail in examples. Both the inventive dopedsemiconducting materials of the present application and the inventivesemiconducting materials of WO2015/097232 show comparable performanceand bring significant improvements over the state of art known up topriority date of the present application.

In the first screening phase, there were (in device of Example 1) tested32 matrix compounds with 5 wt % Mg as dopant. Electron transportmatrices comprising phosphine oxide matrices and having their LUMO levelexpressed in terms of their reduction potential vs. Fc⁺/Fc (measured bycyclic voltammetry in THF) higher than compound B0 (−2.21 V understandardized conditions used) performed better than C1 and C2, in t s ofoperational voltage and/or quantum efficiency of the device, andsignificantly better than matrices lacking the phosphine oxide group,irrespective of their LUMO level. These observations were confirmed alsofor several other divalent metals, namely Ca, Sr, Ba, Sm and Yb.

The results are summarized in Table 1, wherein relative change ofvoltage and efficiency (both measured at current density 10 mA/cm²) iscalculated against the C2/Mg system of previous art taken as thereference. The overall score is calculated by subtraction of relativevoltage change from relative change of efficiency.

TABLE 1 ETL ETL wt % U (U − U_(ref))/U_(ref) EQE (EQE −EQE_(ref))/EQE_(ref) matrix dopant dopant (V) (%) (%) (%) score E1 Li0.5 3.255 −39 5.340 −5 +34 E1 Mg 5 3.2 −40 5.15 −9 +31 E1 Ca 1 3.497 −355.415 −4 +31 E1 Ca 5 3.633 −32 5.235 −7 +25 E1 Ba 1 3.577 −33 6.090 +8+41 E1 Ba 5 3.491 −35 5.560 −1 +34 E2 Li 0.5 3.264 −39 5.345 −5 +34 E2Mg 5 3.56 −34 5.33 −5 +29 E2 Ca 1 3.245 −39 5.750 +2 +41 E2 Ca 5 3.83−29 5.83 +4 +33 E2 Ba 1 6.104 +13 6.245 +14 +1 E2 Ba 5 3.293 −39 6.055+8 +47 E3 Mg 5 3.68 −31 4.68 −17 +14 E4 Mg 5 3.6 −33 3.9 −31 +2 E4 Ca 23.490 −35 5.900 +5 +40 E4 Ba 2 4.020 −25 6.150 +9 +34 E4 Sm 2 3.806 −295.600 0 +29 E4 Yb 2 3.844 −28 5.390 −4 +24 E5 Mg 5 3.29 −29 5.45 −3 +26E6 Mg 5 3.53 −34 7.73 +38 +72 E6 Ca 2 3.350 −37 5.650 +0 +37 E6 Ba 23.710 −31 6.320 +12 +43 E6 Sm 2 3.429 −36 6.040 +7 +43 E6 Yb 2 3.427 −365.965 +6 +42 E7 Mg 5 5.2 −3 6.48 +15 +18 E8 Mg 5 3.36 −37 5.6 0 +37 E8Ca 2 3.26 −39 5.24 −7 +32 E8 Ba 2 3.329 −38 5.990 +6 +44 E9 Mg 5 4.51−16 7.5 +33 +49 E10 Mg 5 3.81 −29 4.7 −17 +12 E11 Mg 5 3.88 −28 4.53 −20+8 E11 Sr 1 3.642 −32 5.500 −2 +30 E11 Sr 3 3.653 −32 5.075 −10 +22 E11Sm 2 4.113 −23 5.365 −5 +18 E11 Sm 5 4.067 −24 4.435 −21 +3 E11 Yb 23.693 −31 5.485 −3 +28 E11 Yb 5 3.796 −29 5.105 −9 +20 B6 Mg 5 3.44 −364.00 −29 +7 B2 Mg 5 5.67 +5 0.66 −89 −94 B4 Ca 2 7.549 +40 0.49 −92 −132B4 Ba 2 9.784 +82 2.260 −60 −142 B4 Sm 2 7.993 +48 1.400 −75 −123 B4 Yb2 8.689 +65 1.960 −65 −130 C1 Mg 5 4.2 −22 2.6 −54 −32 C2 Mg 5 5.4 0 5.60 0 C3 Mg 5 7.11 +32 0.85 −85 −117 C4 Mg 5 8.3 +54 2.32 −59 −114 C5 Mg 56.8 +26 2.9 −49 −75 C6 Mg 5 8.78 +63 3.78 −33 −96 C6 Ca 2 5.500 +2 4.045−28 −30 C6 Ba 2 7.101 +32 3.865 −31 −63 C6 Sm 2 8.167 +52 2.355 −58 −110C6 Yb 2 8.130 +51 3.075 −46 −97 C7 Mg 5 4.17 −22 0.9 −84 −62 C7 Sm 25.362 0 1.680 −70 −70 C7 Yb 2 5.866 +9 1.890 −67 −76 C8 Mg 5 4.17 −221.04 −82 −60 C9 Mg 5 4.2 −22 1 −83 −61 D1 Ca 2 6.731 +25 2.230 −61 −86D1 Ba 2 8.515 +58 2.295 −60 −118 D1 Sm 2 7.972 +48 2.250 −60 −108 D1 Yb2 8.006 +49 2.765 −51 −100

In the second phase of the research, various metals were tested indevice 2 in matrices E1, E2 and C1, with two different ETL thicknesses40 nm (U₁ and U₃) and 80 nm (U₂ and U₄) and with two different dopingconcentrations 5 wt % (U₁ and U₂) and 25 wt % (U₃ and U₄), all forcurrent density 10 mA/cm².

The results summarized in Table 2 led to a preliminary conclusion thatmetals that are able to form stable compounds in oxidation state II areespecially appropriate for n-doping in phosphine oxide matrices despitetheir significantly lower reactivity and higher air stability incomparison with the least reactive alkali metal (Li). From the divalentmetals tested, only zinc having extremely high sum of the first andsecond ionization potential failed as n-dopant, whereas aluminium withtypical oxidation state III gave reasonably low operational voltagesonly if present in the doped ETL in the high 25 wt % concentration thatafforded ETLs with impractically high light absorption. Transmittanceassigned as “OD” that stands for “optical density” is reported in Table2 only for 25 wt % doping concentration (OD₃ for layer thickness 40 nmand OD₄ for layer thickness 80), as the measurements for lower dopingconcentrations suffered from bad reproducibility.

The typically trivalent bismuth failed as n-dopant completely, despiteits ionization potential does not differ much, e.g. from manganese thatshowed, quite surprisingly, good doping action at least in E1.

Low values of differences U₁-U₂ and U₃-U₄ can be assigned to dopedmaterials having high conductivity (voltage of the device depends onlyweakly on the thickness of the doped layer).

TABLE 2 ETL ETL U₁ U₂ U₁ − U₂ U₃ U₄ U₃ − U₄ matrix dopant (V) (V) (V)(V) (V) (V) OD₃ OD₄ E₁ Li 9.042 >10 na 5.814 6.666 0.853 38 43 E₁ Na2.863 2.864 0.001 5.354 7.186 1.832 70 64 E₁ Mg 2.954 2.970 0.016 2.9652.960 0.005 62 33 E₁ Ca 4.625 4.340 −0.286 5.590 9.081 3.491 63 52 E₁ Sr3.650 3.700 0.050 — — — — — E₁ Ba 4.085 4.023 −0.062 4.360 4.567 0.20767 73 E₁ Sm 3.138 3.136 −0.002 7.889 — — 63 61 E₁ Eu — — — 4.090 4.1190.029 — — E₁ Yb 3.022 3.032 0.009 5.578 6.932 1.354 66 68 E₁ Mn 3.38 3.40 0.017 — — — — — E₁ Zn 6.124 8.842 2.718 5.592 7.545 1.954 65 76 E₁Al 7.614 >10 na 3.321 3.301 −0.020  48 31 E₁ Bi 6.129 8.768 2.640 5.4307.275 1.845 56 54 E₂ Li 6.333 8.362 2.029 3.307 3.324 0.017 51 32 E₂ Na3.735 4.533 0.798 >10     >10     na 65 38 E₂ Mg 3.189 3.232 0.043 3.4643.489 0.025 68 72 E₂ Ca 4.426 4.503 0.078 3.911 4.501 0.590 64 50 E₂ Sr3.842 3.832 −0.010 — — — — — E₂ Ba 2.929 2.935 0.006 3.397 3.397 0.00074 71 E₂ Sm 3.610 3.894 0.284 6.053 7.939 1.887 72 63 E₂ Eu — — — 4.5164.838 0.322 — — E₂ Yb 2.932 2.933 0.001 5.442 6.625 1.183 73 65 E₂ Mn6.02  8.09 0.99 — — — — — E₂ Zn 7.898 >10 na 7.000 >10     na 66 71 E₂Al 8.650 >10 na 3.203 3.196 −0.007  39 27 E₁ Bi 7.814 >10 na7.173 >10     na 64 61 C1 Li 6.997 >10 na 6.209 8.314 2.105 72 48 C1 Na— — — 4.417 4.455 0.037 56 31 C1 Mg 4.180 4.178 −0.002 4.174 4.167−0.007  62 57 C1 Ca 4.031 4.104 0.074 3.619 3.616 −0.004  38 21 C1 Sr4.033 4.071 0.0038 — — — — — C1 Ba 3.916 3.909 −0.006 3.969 4.605 0.63663 39 C1 Sm 4.208 4.207 0.000 4.106 4.104 −0.002  63 48 C1 Eu 3.9723.984 0.012 — — — — — C1 Yb 4.017 4.167 −0.003 4.148 4.173 0.025 33 29C1 Mn 4.27  4.26 −0.01 — — — — — C1 Zn 5.084 7.758 2.674 4.699 6.4021.703 57 50 C1 Al 4.152 4.949 0.797 3.135 3.123 −0.011  45 26 C1 Bi4.842 6.355 1.513 4.306 4.603 0.297 59 68

It has been observed matrices with deep LUMO, like C1, the operationalvoltage is often surprisingly higher in devices comprising matrices withthe LUMO levels in the range according to invention, despite goodconductivity of many doped semiconducting materials based on C1.Apparently, the good conductivity of a semiconducting material is not asufficient condition for low operational voltage of the devicecomprising it. Based on this finding, it is supposed that dopedsemiconducting materials according to this invention enable, besides thereasonable conductivity, also efficient charge injection from the dopedlayer in the adjacent layer.

In the third research phase, the observed effects were confirmed inOLEDs of Example 3 comprising alternative emitter systems and furtherembodiments of the invention described in examples 4-7 were implemented.The achieved results summarized in the Table 3 confirmed the surprisingsuperiority of phosphine oxide ETL matrices having higher LUMO levels(closer to vacuum level), despite these matrices should be moredifficult to dope with the relatively weakly reducing metals used in thepresent invention in comparison with the phosphine oxide matrices of theprevious art (like C1) which were thought to be dopable with Mg owing totheir deeper LUMO (further away from vacuum level) and specificstructure comprising the metal complexing unit.

This series of experiments confirmed that also with other emitters, thematrix compounds E1 and E2 having rather high LUMO energy levels performbetter than other phosphine oxide matrix compounds, and much better incomparison with matrices lacking the phosphine oxide group.

These results showed that if combined with phosphine oxide matriceshaving sufficiently high LUMO levels, even substantially air stablemetals, possessing moreover further technically advantageous featureslike good evaporability, can afford electrically doped semiconductivematerials and devices that perform equally well or even better thandevices available in the art.

TABLE 3 ETL ETL wt % U (U-U_(ref))/U_(ref) EQE (EQE-EQE_(ref))/ LELmatrix dopant dopant (V) (%) (%) EQE_(ref) (%) score ABH- E1 Mg 5 3.498−35 6.640 +18 +53 112/ E2 Mg 5 3.751 −30 5.975 +6 +36 NUBD- C1 Mg 54.545 −15 3.905 −30 −15 369 C10 Mg 5 — — 0 no light — Two- E1 Mg 5 3.480−35 7.660 +36 +71 colour E2 Mg 5 3.83 −29 6.67 +19 +48 fluoresc. C1 Mg 54.970 −8 4.470 −20 −12 white* C10 Mg 5 6.950 +28 0.820 −85 −113 Spiro-E1 Mg 5 3.331 −38 6.19 +10 +48 Pye/ E1 Ca 5 3.311 −38 4.46 −20 +18 BCzVBE1 Ba 12 3.087 −42 3.44 −39 +3 E1 Sm 5 3.318 −38 4.53 −19 +19 E2 Mg 53.480 −35 6.08 +8 +43 E2 Ca 5 3.497 −35 3.56 −37 +1 E2 Ba 5 3.090 −423.59 −36 +6 C7 Mg 5 3.679 −31 0.32 −94 −63 C7 Ca 5 3.647 −33 0.52 −90−57 *ABH-112/NUBD-369 + ABH-036/NRD129 (Sun Fine Chemicals)

Then, the focus returned to the starting point. The goal was to make theredox potential of the matrix compound significantly more negative incomparison with compound C2, and test whether if the LUMO level of thematrix compound approaches closer to the zero (vacuum) energy level inthe absolute energy scale, it will have similarly positive effect inphosphine oxide compounds comprising a small conjugated system of lessthan 10 delocalized electrons as was previously observed in the matrixcompounds comprising larger systems of delocalized electrons. This taskwas accomplished relatively easily with commercially available compoundsA1-A4. All these compounds have redox potentials that are difficult tomeasure by the standard procedure using THF as a solvent, because theirvalues are more negative than for compound B7.

Based on mostly discouraging results of previous experiments with C2analogs and salt additives, rather negative results were expected frommetal doping in matrices which are free of a conjugated system ofdelocalized electrons or comprising less than 10 delocalized electronsin a conjugated system. Contrary to these expectations, it wassurprisingly found that sufficiently strong dopants can providesemiconducting materials of good quality even with compounds havingconjugated systems of delocalized electrons that are as small as meresix-electron Hückel systems in isolated aromatic or heteroaromaticrings, provided that the compound still comprises polar groups selectedfrom phosphine oxide and diazole. Subsequently, it was confirmed thatsuch simple two-component semiconducting materials consisting of metaland the first compound having only six delocalized electrons in aconjugated system can be advantageously mixed with a second compoundcomprising larger conjugated systems of delocalized electrons withoutloss of performance, even though the second compound does not compriseany polar group at all. It was further surprisingly found that, contraryto previous experience with electron transport compounds comprising bothpolar group and the conjugated system of at least ten delocalizedelectrons, in matrices comprising polar group and a conjugated system ofless than 10 delocalized electrons or free of the conjugated system ofdelocalized electrons, there is no significant difference anymorebetween the doping performance of divalent electropositive metals on onehand and other electropositive metals like alkali metals and typicallytrivalent rare earth metals like Sc, Y, La or Lu on the other hand. Inthis sense, it seems unnecessary to make any speculations about theextent of charge transfer between the doping electropositive element andthe matrix and try to divide the electropositive elements used asn-dopants in semiconducting materials according to invention in groupsof “strong” and “weak” dopants. It is, therefore, supposed that theelectropositive element is still at least partially present in itssubstantially elemental form in the inventive semiconducting materials,and that the favourable results observed in matrices comprising polarphosphine oxide or diazole groups are to be linked to specificinteractions of these polar groups with atoms or atom clusters of theelectropositive element.

Finally, subsequent experiments with matrix compounds comprising largersystems of delocalized electrons confirmed that with matrices havingmore negative reduction potentials than 4,7-diphenyl-1,10-phenanthrolineand with electropositive elements selected from Li, Na, K, Be, Sc, Y,La, Lu, Ti and V, excellent OLED performance can be achieved basicallyirrespective of the presence and/or extent of the conjugated system ofdelocalized electrons in the substantially organic electron transportcompound comprises the polar group as defined in the present invention.The OLED results achieved in devices of Example 1 are presented(together with results of the first research phase) in the Table 1,other results are presented below in Examples.

VI. EXAMPLES

Auxiliary Materials

Auxiliary Procedures

Cyclic Voltammentry

The redox potentials given at particular compounds were measured in anargon deaerated, dry 0.1M THF solution of the tested substance, underargon atmosphere, with 0.1M tetrabutylammonium hexafluorophosphatesupporting electrolyte, between platinum working electrodes and with anAg/AgCl pseudo-standard electrode, consisting of a silver wire coveredby silver chloride and immersed directly in the measured solution, withthe scan rate 100 mV/s. The first run was done in the broadest range ofthe potential set on the working electrodes, and the range was thenadjusted within subsequent runs appropriately. The final three runs weredone with the addition of ferrocene (in 0.1M concentration) as thestandard. The average of potentials corresponding to cathodic and anodicpeak of the studied compound, after subtraction of the average ofcathodic and anodic potentials observed for the standard Fc⁺/Fc redoxcouple, afforded finally the values reported above. All studiedphosphine oxide compounds as well as the reported comparative compoundsshowed well-defined reversible electrochemical behaviour.

Synthesis Examples

The synthesis of phosphine oxide ETL matrix compounds is well describedin many publications, besides the literature cited at particularcompounds listed above and describing typical multistep procedures usedfor these compounds, the compound E6 was prepared, according to Bull.Chem. Soc. Jpn., 76, 1233-1244 (2003), quite specifically by an anionicrearrangement of the compound E2.

For yet unpublished compounds, the typical procedures were used, asexemplified below specifically for the compounds E5 and E8. Allsynthesis steps were carried out under argon atmosphere. Commercialmaterials were used without additional purification. Solvents were driedby appropriate means and deaerated by saturation with argon.

Synthesis Example 1 [1,1′:4′,1″-terphenyl]-3,5-diylbis-diphenylphosphineoxide (E5) Step 1: 3,5-dibromo-1,1′:4′,1″-terphenyl

All components (10.00 g (1.0 eq, 50.50 mmol)[1,1′-biphenyl]-4-yl-boronic acid, 23.85 g (1.5 eq, 75.75 mmol)1,3,5-tribromobenzene, 1.17 g (2.0 mol %, 1.01 mmol) tetrakis(triphenylphosphine)palladium(0), 10.70 g (2 eq, 101 mmol) sodium carbonate in 50mL water, 100 mL ethanol and 310 mL toluene) were mixed together andstirred at reflux for 21 hours. The reaction mixture was cooled to roomtemperature and diluted with 200 mL toluene (three layers appear). Theaqueous layer was extracted with 100 mL toluene, the combined organiclayers were washed with 200 mL water, dried and evaporated to dryness.The crude material was purified via column chromatography (SiO₂,hexane/DCM 4:1 v/v) The combined fractions were evaporated, suspended inhexane and filtered off to give 9.4 g of a white glittering solid (yield48%, HPLC purity 99.79%).

Step 2: [1,1′:4′,1″-terphenyl]-3,5-diylbis-diphenylphosphine oxide

All components (5.00 g (1.0 eq, 12.9 mmol)3,5-dibromo-1,1′:4′,1″-terphenyl from the previous step, 12.0 g (5.0 eq,64.4 mmol) diphenyl phosphine, 114 mg (5 mol %, 6.44×10⁻⁴ mol)palladium(II) chloride, 3.79 g (3.0 eq, 38.6 mmol) potassium acetate and100 ml N,N-dimethylformamide) were mixed together and stirred at refluxfor 21 hours. Then the reaction mixture was cooled to room temperature;water was added (100 mL) and the mixture was stirred for 30 min, thenfiltered off. The solid was re-dissolved in DCM (100 mL), H₂O₂ (30 wt %aqueous solution) was added dropwise, and the solution was stirredovernight at room temperature. Then the organic layer was decanted,washed with water (100 mL) twice, dried over MgSO₄, and evaporated todryness. The resulting oil was triturated in hot MeOH (100 mL) whichinduced the formation of a solid. After filtration hot, the resultingsolid was rinsed with MeOH and dried, yielding 9.7 g of crude product.The crude material was re-dissolved in DCM and chromatographed on ashort silica column, elution with ethyl acetate. After evaporation ofthe eluate to dryness, the resulting solid was triturated in hot MeOH(100 mL), followed by trituration in hot ethyl acetate (50 mL). Afterdrying, the desired compound was obtained in 70% yield (5.71 g).Finally, the product was purified using vacuum a sublimation.

The pure sublimed compound was amorphous, with no detectable meltingpeak on the DSC curve, glass transition onset at 86° C., and started todecompose at 490° C.

Synthesis Example 2(9,9-dihexyl-9H-fluorene-2,7-diyl)bis-diphenylphosphine oxide (E8)

2,7-Dibromo-9,9-dihexylfluorene (5.00 g, 1.0 eq, 10.2 mmol) as placed ina flask and deaerated with argon. Then anhydrous THF (70 mL) was added,and the mixture was cooled to −78° C. 9.7 mL (2.5M solution in hexanes,2.4 eq, 24.4 mmol) n-butyllithium were then added dropwise; theresulting solution was stirred for 1 h at −78° C., and thenprogressively warmed to −50° C. After slow addition of purechlorodiphenylphosphine (4.0 mL, 2.2 eq, 22.4 mmol), the mixture wasleft to stir overnight till room temperature. MeOH (20 mL) was added toquench the reaction, and the solution was evaporated to dryness. Thesolid was re-dissolved in DCM (50mL), H₂O₂ (30 wt % aqueous solution, 15mL) was added dropwise, and the mixture left under stirring. After 24 h,the organic phase was separated, washed subsequently with water andbrine, dried over MgSO₄, and evaporated to dryness. Purification bychromatography (silica, gradient elution from hexane/EtOAc 1:1 v/v toneat EtOAc) provided the desired compound in 34% yield (2.51 g). Thematerial was then further purified by vacuum sublimation.

The pure sublimed compound was amorphous, with no detectable meltingpeak on the DSC curve, and decomposed at 485° C.

Synthesis Example 3Diphenyl-(3-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide(E14)

Step 1.

Synthesis of 2-bromospiro[fluorene-9,9′-xanthene]

2-Bromo-9-fluorenone (10.00 g, 1.0 eq, 38.6 mmol) and phenol (34.9 g,9.6 eq., 0.37 mol) were placed in a two-necked flask and degassed withargon. Methanesulfonic acid (10.0 mL, 4.0 eq, 0.15 mol) was added, andthe resulting mixture was refluxed for 4 days at 135° C. After coolingto room temperature, DCM (80 mL) and water (130 mL) were added. Uponstirring, the material precipitates. After filtration and abundantwashing with MeOH, it was finally triturated in hot EtOH (60 mL) for 1h, which after filtration afforded the desired compound (11.0 g,69%), >99% purity according to GCMS.

Step 2.

Synthesis ofdiphenyl(3-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide

2-Bromospiro[fluorene-9,9′-xanthene] (10.0 g, 1.2 eq, 24.3 mmol) wascharged in a two-necked flask, degassed with argon, and dissolved inanhydrous THF (240 mL). To this solution were added Mg⁰ (827 mg, 1.4 eq,34.0 mmol), followed by iodomethane (414 mg, 0.12 eq., 2.92 mmol), andthe resulting mixture was refluxed for 2 hours. Then, this Grignardsolution was cannulated to an anhydrous solution of(3-bromophenyl)diphenylphosphine oxide (7.23 g, 1.0 eq., 20.3 mmol) and[1,3-bis(diphenylphosphino)propane]nickel(II) chloride (263 mg, 2.0 mol%, 0.49 mmol) in THF (200 mL). The resulting mixture was refluxedovernight after which it was quenched by addition of water (5 mL). Theorganic solvent was removed under reduced pressure, and the compoundextracted with CHCl₃ (200 mL) and water (100 mL); the organic phase wasdecanted, her washed with water (2×200 mL), dried over MgSO₄ andevaporated to dryness. The crude product was filtered over silica; uponelution with n-hexane/DCM 2:1, apolar impurities was removed, while thedesired was isolated using pure DCM. After removal of the DCM, theproduct was triturated in ethylacetate (100 mL), filtered off, and driedunder vacuum yielding the title compound (7.5 g, 61%). Finally, theproduct was purified by sublimation (78% yield).

Material Properties:

DSC: Melting Point: 264° C. (Peak), Sublimed Material

CV: LUMO vs. Fc (THF): −2.71 V (Reversible)

Synthesis Example 4Diphenyl-(4-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide(E15)

2-Bromospiro[fluorene-9,9′-xanthene] (10.0 g, 1.2 eq, 24.3 mmol) wascharged in a two-necked flask, degassed with argon, and dissolved inanhydrous THF (240 mL). To this solution were added Mg⁰ (827 mg, 1.4 eq,34.0 mmol), followed by iodomethane (414 mg, 0.12 eq., 2.92 mmol), andthe resulting mixture was refluxed for 2 hours. Then, this Grignardsolution was cannulated to an anhydrous solution of(4-bromophenyl)diphenylphosphine oxide (7.23 g, 1.0 eq., 20.3 mmol) and[1,3-bis(diphenylphosphino)propane]nickel(II) chloride (263 mg, 2.0 mol%, 0.49 mmol) in THF (200 mL). The resulting mixture was refluxedovernight after which it was quenched by addition of water (5 mL). Theorganic solvent was removed under reduced pressure, and the compoundextracted with DCM (2 L) and water (500 mL); the organic phase wasdecanted, dried over MgSO₄ and evaporated to dryness. The crude productwas purified by chromatography over silica, elution with DCM/MeOH 99:1.The fractions containing the product were merged and evaporated todryness. The resulting solid was then triturated in ethylacetate (50mL), filter off, and dried under vacuum yielding the title compound (4.0g, 32%). Finally, the product was purified by sublimation (77% yield).

Material Properties:

DSC: Melting Point: 255° C. (Peak), Sublimed Material

CV: LUMO vs. Fc (THF) −2.65 V (Reversible)

Synthesis Example 5 9-Phenyltribenzo[b,d,f]phosphepine-9-oxide (E16)

The preparation was accomplished according to following scheme, with thelast rearrangement step analogous to preparation of compound E6 by theprocedure published in Bull. Chem. Soc. Jpn., 76, 1233-1244 (2003):

CV: LUMO vs. Fc (THF): −2.91 V (Reversible)

Device Examples

Inventive and Comparative Example 1 Blue OLED

A first blue emitting device was made by depositing a 40 nm layer ofHTM2 doped with PD2 (matrix to dopant weight ratio of 97:3 wt %) onto anITO-glass substrate, followed by a 90 nm undoped layer of HTM1.Subsequently, a blue fluorescent emitting layer of ABH113 (Sun FineChemicals) doped with NUBD370 (Sun Fine Chemicals) (97:3 wt %) wasdeposited with a thickness of 20 nm. A 36 nm layer of the testedcompound was deposited on the emitting layer together with the desiredamount of the metallic element (usually, with 5 wt % Mg) as ETL.Subsequently, an aluminium layer with a thickness of 100 nm wasdeposited as a cathode.

The observed voltages and quantum efficiencies at a current density 10mA/cm² are reported in the Table 1. The devices with Li-doped ETLs basedon compounds E1 or E2 performed comparably well with best materials ofWO2015/097232 doped with divalent metals.

Comparative Example 2 Organic Diode

A similar device was produced as in Example 1, with the difference thatthe emitter was omitted, and each combination matrix-dopant was testedin two different thicknesses of the ETL (40 and 80 nm) and with twodifferent dopant concentrations (5 and 25 wt %). The observed voltagesat the current density 10 mA/cm² and, wherever measured, opticalabsorbances of the device, are reported in the Table 2.

Comparative Example 3 Blue or White OLED

A similar device was produced as in Example 1, with the difference thatthere were combined various compositions of semiconducting materials inthe ETL with various emitter systems. The results were evaluatedsimilarly as in Example 1 and are summarized in Table 3.

Comparative Example 4 Blue OLED

In device of Example 1, A1 cathode was replaced with the sputteredindium tin oxide (ITO) cathode in combination with the Mg or Ba dopedETL. The results showed that ETLs based on divalent metal dopedphosphine oxide matrices having redox potentials vs Fc+/Fc in the rangefrom −2.24 V to −2.81 V are applicable also in top emitting OLEDs withcathode made of transparent semiconductive oxide.

Comparative Example 5 Transparent OLED

In transparent devices having p-side (substrate with ITO anode, HTL,EBL) as in Example 1, and sputtered 100 nm thick ITO cathode as inExample 4, polymeric emitting layer comprising blue emitting polymer(supplied by Cambridge Display Technology) was successfully tested. Theresults reported in Table 4 (together with the n-side composition of thedevice, which in all cases comprised a 20 nm thick HBL consisting of F2and ETL1 consisting of E2 and D3 in weight ratio 7:3 and having athickness given in the table) show that ETLs based on phosphine oxidecompounds doped with divalent metals are applicable even with polymericLELs having very high LUMO levels about −2.8 V (in terms of their redoxpotential vs. Fc⁺/Fc reference). Without metal doped ETL, the deviceshad (at current density 10 mA/cm²) very high voltages, even when EILsmade of pure metal were deposited under the ITO electrode.

TABLE 4 ETL1 ETL2 (nm) (30 nm) EIL U (V) EQE (%) CIE1931x CIE1931y 20E2/Mg 8:2 5 nm Mg—Ag (9:1) 4.2 1.6 0.16 0.11 10 E2/Mg 9:1 5 nm Ba 4.51.3 0.16 0.13 20 E2/Mg 8:2 5 nm Al 5.4 1.1 0.16 0.14 5 E2/Ba 8:2 — 4.61.3 0.16 0.18 20 — 5 nm Mg—Ag (9:1) 7.5 1.8 0.17 0.22 10 — 5 nm Ba 6.42.2 0.10 0.13

Comparative Example 6 Metal Deposition Using Linear Vaporization Source

Evaporation behaviour of Mg in a linear evaporation source was tested.It was demonstrated that Mg can be deposited from linear sources withthe rate as high as 1 nm/s without spitting, whereas point evaporationsources spit Mg particles at the same deposition rate significantly.

Comparative Example 7 Metal+Metal Salt Electrical Doping in the Same ETL

Mixed ETL comprising a matrix combined with LiQ+either Mg or W₂(hpp)₄ acombined two-component doping system showed the superiority of thesalt+metal combination.

Comparative Example 8 Tandem White OLED

On an ITO substrate, following layers were deposited by vacuum thermalevaporation: 10 nm thick HTL consisting of 92 wt % auxiliary material F4doped with 8 wt % PD2, 135 nm thick layer of neat F4, 25 nm thick blueemitting layer ABH113 (Sun Fine Chemicals) doped with NUBD370 (Sun FineChemicals) (97:3 wt %), 20 nm thick layer ABH036 (Sun Fine Chemicals),10 nm thick CGL consisting of 95 wt % compound E12 doped with 5 wt % Mg,10 nm thick HTL consisting of 90 wt % auxiliary material F4 doped with10 wt % PD2, 30 nm thick layer of neat F4, 15 nm thick layer of neat F3,30 nm thick proprietary phosphorescent yellow emitting layer, 35 nmthick ETL of auxiliary material F5, 1 nm thick LiF layer and aluminiumcathode. The diode operated at 6.81 V had EQE 24.4%.

Comparative Example 9 Tandem White OLED

The example 8 was repeated with Yb in the CGL instead of Mg. The diodeoperated at 6.80 V had EQE 23.9%.

Comparative Example 10 Tandem White OLED

The example 9 was repeated with compound E6 instead of E12 in the CGL.The diode operated at 6.71 V had EQE 23.7%.

Inventive and Comparative Example 11 Charge Injection into Adjacent orAdmixed High-LUMO ETM in a Blue OLED

Example 1 was repeated with following modifications:

On the ITO substrate, 10 nm thick HTL consisting of 92 wt % auxiliarymaterial F4 doped with 8 wt % PD2 followed by 130 nm thick layer of neatF4 were deposited by VTE. On top of the same emitting layer as inexample 1, a 31 nm thick HBL of F6 and on top of it the doped ETLaccording to Table 5 were deposited subsequently, followed with thealuminium cathode. All deposition steps were done by VTE under pressurebelow 10⁻² Pa.

TABLE 5 Mg 36 nm Yb Ba Li ETM:Mg (95:5) 36 nm 36 nm 36 nm V at ETM:Yb(95:5) ETM:Ba (95:5) ETM:Li (99.5:0.5) ETM E₀ V 10 mA/cm² V at 10 mA/cm²V at 10 mA/cm² V at 10 mA/cm² E5 −2.58 4.2 3.7 E6 −2.62 6.1 3.5 E7−2.81 >5.2 3.7 E13 −2.78 3.9 3.2 3.2 3.4 E14 −2.71 3.3 A2 <−3.10 3.9 3.93.3 A4 <−3.10 4.1 3.2 A2:F6 <−3.10:−2.63 3.3 3.3 A2:B10 <−3.10:−2.91 3.93.7 C11 −2.45 >10.0 5.9 5.3

The experiments convincingly showed that compounds E5, E6, E7, E13 andE14 as well as A2 and A4 and their mixtures with ETMs which are free ofa polar group provided very good electron injection into adjacent F6layer, despite its highly negative reduction potential. Due to highlynegative reduction potential and low polarity of the F6 layer, the modeldevice mimicks also the properties of devices comprising emitting layersmade of light emitting polymers.

Comparative Example 12 Charge Injection into Adjacent or AdmixedHigh-LUMO ETM in a Blue OLED

Example 11 was repeated under replacement F6 in HBL with B10.Composition of ETLs and results are shown in Table 6.

TABLE 6 Yb Ba 36 nm Yb (EIL) Ba (EIL) 36 nm ETM:Yb (95:5) 2-5 nm 2 nmETM:Ba (95:5) V at ETM:Yb (95:5) ETM:Ba (95:5) ETM E₀ V V at 10 mA/cm²10 mA/cm² V at 10 mA/cm² V at 10 mA/cm² E5 −2.58 E6 −2.62 8.1 E7 −2.81E13 −2.78 5.4 A2 <−3.10 5.6 6.8 5.9 A4 <−3.10 A2:F6 <−3.10:−2.63 7.1 7A2:B10 <−3.10:−2.91 6.9 7.1

The results showed that semiconducting materials based on phosphineoxide matrices doped with divalent metals allow an efficient electroninjection also into a CBP layer having even more negative redoxpotential than the HBL matrix of the previous example.

Inventive and Comparative Example 13 Applicability of Inventive andComparative Semiconducting Materials in Very Thick ETLs

Example 11 was repeated with ETLs having thickness 150 nm. The resultsare shown in Table 7.

TABLE 7 Mg 150 nm Yb Li ETM:Mg (95:5) 150 nm Ba 150 nm V at ETM:Yb(95:5) 150 nm ETM:Li (99.5:0.5) ETM E₀ V 10 mA/cm² V at 10 mA/cm² ETM:Ba(95:5) V at 10 mA/cm² E5 −2.58 E6 −2.62 7.50 3.6 E7 −2.81 E13 −2.78 3.33.2 3.4 E14 −2.71 3.3 A2 <−3.10 3.8 A4 <−3.10 3.5 A2:F6 <−3.10:−2.63 3.3A2:B10 <−3.10:−2.91 4.8 C11 −2.45 5.2

Comparison with Table 5 demonstrates that devices utilizing in ETLsphosphine oxide compounds with highly negative reduction potentials E5,E6, E7, E13, E14, A2 d A4 show practically the same operational voltagesas devices of Example 11, despite the thickness of the ETL increasedmore than four times. The experiment shows that lithium-doped materialaccording to present invention represents viable alternative to bestmaterials based on divalent metals and equally well enables easilytuning the size of optical cavity in electronic devices comprisingemitting layers with very negative redox potentials, like light emittingpolymers.

The features disclosed in the foregoing description, in the claims andin the accompanying drawings may both separately and in any combinationbe material for realizing the invention in diverse forms thereof.Reference values of physico-chemical properties relevant for the presentinvention (first and second ionization potential, normal boiling point,standard redox potential) are summarized in Table 8.

TABLE 8 I_(p) ^(I) I_(p) ^(II) ΣI_(p) ^(I-II) b.p.¹ Element eV² eV² eV²° C. E₀ V Li 5.391 75.640 81.031 1330 −3.04 Na 5.139 47.286 52.425 890−2.713 Mg 7.646 15.035 22.681 1110 −2.372 Al 5.986 18.829 24.815 2470−1.676 Ca 6.113 11.872 17.985 1487 −2.84 Mn 7.434 15.640 23.074 2100−1.18 Zn 9.394 17.964 27.358 907 −0.793 Sr 5.695 11.030 16.725 1380−2.89 Ba 5.212 10.004 15.216 1637 −2.92 Sm 5.644 11.07 16.714 1900 ** Eu5.670 11.241 16.911 1440 −1.99 Yb 6.254 12.176 18.430 1430 −2.22 Bi7.286 16.69 23.976 1560 0.317 ¹Yiming Zhang, Julian R. G. Evans,Shoufeng Yang: Corrected Values for Boiling Points and Enthalpies ofVaporization of Elements in Handbooks. From: Journal of Chemical &Engineering Data. 56, 2011, p. 328-337; the values fit with values givenin articles for individual elements in current German version ofWikipedia.²http://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_%28data_page%29

USED ABBREVIATIONS

CGL charge generating layer

CV cyclic voltammetry

DCM dichloromethane

DSC differential scanning calorimetry

EIL electron injecting layer

EQE external quantum efficiency of electroluminescence

ETL electron transporting layer

ETM electron transport matrix

EtOAc ethyl acetate

Fc⁺/Fc ferrocenium/ferrocene reference system

h hour

HBL hole blocking layer

HIL hole injecting layer

HOMO highest occupied molecular orbital

HTL hole transporting layer

HTM hole transport matrix

ITO indium tin oxide

LUMO lowest unoccupied molecular orbital

LEL emitting layer

LiQ lithium 8-hydroxyquinolinolate

MeOH methanol

mol % molar percent

mp melting point

OLED organic light emitting diode

QA quality assurance

RT room temperature

THF tetrahydrofuran

UV ultraviolet (light)

vol % volume percent

v/v volume/volume (ratio)

VTE vacuum thermal evaporation

wt % weight (mass) percent

1. Electronic device comprising at least one light emitting layerbetween an anode and a cathode, the device further comprising betweenthe cathode and the anode at least one mixed layer comprising (i) insubstantially elemental form, an electropositive element selected fromLi, Na, K, Be, Sc, Y, La, Lu, Ti, or V, and (ii) at least onesubstantially covalent electron transport matrix compound comprising atleast one polar group selected from a) phosphine oxide group, whereinthe reduction potential of the substantially covalent electron transportmatrix compound, if measured by cyclic voltammetry under the sameconditions, has the value which is more negative than the value obtainedfor at least one of 4,7-diphenyl-1,10-phenanthroline, (9phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 3phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, pyrene,and [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) or b)diazole group, wherein the reduction potential of the substantiallycovalent electron transport matrix compound, if measured by cyclicvoltammetry under the same conditions, has the value which is morenegative than the value obtained for at least one of4,7-diphenyl-1,10-phenanthroline, (9phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 3phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, pyrene,and [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide). 2.Electronic device according to claim 1, wherein the electropositiveelement is selected from Li, Sc, or Y.
 3. Electronic device according toclaim 1, wherein the electron transport matrix compound comprises aconjugated system of at least ten delocalized electrons.
 4. Electronicdevice according to claim 3, wherein the electron transport matrixcompound comprises at least one aromatic or heteroaromatic ring. 5.Electronic device according to claim 3, wherein the electron transportmatrix compound comprises at least two aromatic or heteroaromatic ringswhich are either linked by a covalent bond or condensed.
 6. Electronicdevice according to claim 1, wherein the molar ratio of theelectropositive element to the electron transport compound is lower than0.5.
 7. Electronic device according to claim 1, wherein the molar ratioof the electropositive element to the electron transport compound ishigher than 0.01.
 8. Electronic device according to claim 1, wherein thephosphine oxide polar group is part of a substantially covalentstructure comprising at least three carbon atoms directly attached tothe phosphorus atom of the phosphine oxide group and having overallcount of covalently bound atoms in the range 16-250 atoms.
 9. Electronicdevice according to claim 1, wherein the phosphine oxide polar group isselected from phosphine oxide substituted with three monovalenthydrocarbyl groups or one divalent hydrocarbylene group forming with thephosphorus atom a ring and one monovalent hydrocarbyl group, and theoverall count of carbon atoms in the hydrocarbyl groups and thehydrocarbylene group is 8-80.
 10. Electronic device according to claim1, wherein the diazole polar group is an imidazole group.
 11. Electronicdevice according to claim 3, wherein the conjugated system of at least10 delocalized electrons is comprised in a C₁₄-C₅₀-arene or a C₈-C₅₀heteroarene structural moiety.
 12. Electronic device according to claim1, further comprising a metal salt additive consisting of at least onemetal cation and at least one anion.
 13. Electronic device according toclaim 1, wherein the light emitting layer comprises a light emittingpolymer.
 14. Electronic device according to claim 1, wherein the mixedlayer is adjacent to the cathode or is comprised in a charge generatinglayer.
 15. Electronic device according to claim 1, wherein the cathodeis a transparent conductive oxide cathode.
 16. Process for manufacturingthe electronic device of claim 1, the process comprising at least onestep wherein (i) an electropositive element selected from Li, Na, K, Be,Sc, Y, La, Lu, Ti, or V, and (ii) at least one substantially covalentelectron transport matrix compound comprising at least one polar groupselected from a) phosphine oxide group, wherein the reduction potentialof the substantially covalent electron transport matrix compound, ifmeasured by cyclic voltammetry under the same conditions, has the valuewhich is more negative than the value obtained for at least one of4,7-diphenyl-1,10-phenanthroline, (9phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphineoxide),(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 3phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, pyrene,and [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) or b)diazole group, wherein the reduction potential of the substantiallycovalent electron transport matrix compound, if measured by cyclicvoltammetry under the same conditions, has the value which is morenegative than the value obtained for at least one of4,7-diphenyl-1,10-phenanthroline, (9phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide),(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide),1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 3phenyl-3H-benzo[b]dinaphto[2,1-d:1′,2′-f]phosphepine-3-oxide, pyrene,and [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide), arecoevaporated and codeposited under reduced pressure to form the mixedlayer, and the electropositive element is deposited in its elemental orsubstantially elemental form.
 17. Process according to claim 16, whereinthe electropositive element is evaporated from its elemental orsubstantially elemental form.
 18. Process according to claim 16, whereinthe pressure is lower than 10⁻² Pa.
 19. Process according to claim 16,wherein the electropositive element is Li and the ratio of massdeposition rate of Li to overall mass deposition rate of the electrontransport matrix is maintained within the range 0.0005-0.0080. 20.Compound having the structure according to formula (I)